The present invention generally relates to reproduced signal switching circuits for reproducing apparatuses having rotary heads for special reproduction, and more particularly to a reproduced signal switching circuit which obtains a continuous reproduced signal by switching signals reproduced by rotary heads for special reproduction, during a special reproduction in which the reproduction is carried out with a tape moving speed which is different from the tape moving speed employed during a normal reproduction.
Generally, in an apparatus which uses rotary heads to record and reproduce a video signal on and from tracks which are formed obliquely to the longitudinal direction of a magnetic tape, a special reproduction is sometimes carried out with a tape moving speed (hereinafter simply referred to as a tape speed) which is different from the tape speed employed during a normal reproduction. The special reproduction includes a quick-motion reproduction in which the tape speed is faster than the tape speed employed during the normal reproduction, a slow-motion reproduction in which the tape speed is slower than the tape speed employed during the normal reproduction, and a still picture reproduction in which the tape is stationary. Because the tape speed employed during the special reproduction is different from the tape speed employed during the normal reproduction, the inclination angle of scanning loci of the rotary heads with respect to the longitudinal direction of the tape during the special reproduction becomes different from the inclination angle of the scanning loci of the rotary heads at the time of the normal reproduction. As a result, during the special reproduction, the tracks which are to be scanned by the rotary heads are not scanned in full. In other words, some parts of the tracks remain unscanned by the rotary heads during the special reproduction, and the level of the reproduced signal decreases when the rotary heads do not scan over such track parts. Accordingly, there is a type of a recording and/or reproducing apparatus which is provided with rotary heads exclusively for the special reproduction, in order to minimize the unscanned track parts and reduce the decrease in the level of the reproduced signal during the special reproduction. The rotary heads exclusively for the special reproduction, have widths which are greater than the widths of the rotary heads which are used during the normal reproduction (and usually used also for the recording). In this type of a recording and/or reproducing apparatus, a pair of rotary heads exclusively for the special reproduction, are mounted on a rotary body such as a rotary drum, at positions angularly shifted with respect to a pair of rotary heads for the normal reproduction.
On the other hand, the signals reproduced by the pair of reproducing rotary heads must be converted into a continuous reproduced signal. In order to perform this conversion, a switching signal is formed by use of pulses which are detected responsive to the rotation of the rotary body which is mounted with the reproducing rotary heads, and the signals reproduced by the reproducing rotary heads are switched by use of the switching signal. A signal picked up from a stationary pickup head which cooperates with magnets mounted on another rotary body which rotates unitarily with the rotary body such as the rotary drum, is used to form the switching signal. The positions of the magnets which cooperate with the stationary pickup head, the rotary heads for the normal reproduction, and the rotary heads exclusively for the special reproduction, differ on the respective rotary bodies. For this reason, the switching signal is obtained by delaying the signal which is picked up by the stationary pickup head by a delay time corresponding to the positional differences.
A conventional reproduced signal switching circuit is designed to switch elements which are connected to time constant circuits of monostable multivibrators which delay the signal picked up by the stationary pickup head, so as to switch the time constants of the time constant circuits and switch the delay times of the monostable multivibrators between the normal reproduction and the special reproduction.
However, the tape speed is different depending on the kind of special reproduction. Hence, when the rotational speed of the rotary heads are maintained the same for each of the kinds of special reproduction, the relative linear speeds of the rotary heads with respect to the tape will vary depending on the tape speed. When the relative linear speeds of the rotary heads with respect to the tape vary, the frequency of a horizontal synchronizing signal within a video signal which is reproduced by the rotary heads becomes different from the regular horizontal synchronizing signal frequency, and it becomes impossible to obtain a satisfactory reproduced picture. Thus, the rotational speed of the rotary body which is mounted with the rotary heads, may be varied, so that the relative linear speeds of the rotary heads with respect to the tape during the special reproduction become the same as the relative linear speeds of the rotary heads at the time of the normal reproduction.
When the rotational speed of the rotary body which is mounted with the rotary heads, is varied, it is necessary to change the timing with which the signals reproduced by the rotary heads are switched so as to obtain the continuous reproduced signal. However, the timing with which the signals reproduced by the rotary heads are switched, is fixed by the time constants of the time constant circuits. For this reason, when the switching of the reproduced signals is performed by the switching signal in this case, the switching does not take place at the correct position (that is, at a position within a vertical blanking period of the reproduced video signal). In an extreme case, there is a problem in that a vertical blanking part appears in the reproduced picture.